As far as I am concerned, the decision is made. Stick the socket in there with an extension and carefully move it with my fingers, wihtout a ratchet attached. If the stud is broken, you will be able to tell.
Cliff, I may get back to you on the tool offer for if I need something more exotic than a 10mm allen socket. As you say, of course I need that as a permanent tool with this car.
Cheers, George